In several technical fields there is a need for a simple and inexpensive flowmeter that is nevertheless accurate and reliable. A typical example of the fields in which a need exists for such a flowmeter is in apartment houses or a district of single-family houses, where demands for economies and a fair allocation of fuel costs between the different consumers have arisen as a result of sharp increases in the prices of fuel oil and other fuels during recent years. The demands just mentioned are not met by the known flowmeters containing a number of rotating parts. On the other hand, the requirements for simplicity are fulfilled by flowmeters that incorporate a vane-like or flap-like element that is set in oscillatory motion by the action of the medium flowing past it, the frequency of this motion being measured and converted to a measure of the flow.
The present invention relates to a flowmeter of the last-mentioned category. However, known flowmeters of this type have a number of serious limitations, the most important of which is that the measuring range, within which the accuracy of measurement has an acceptable magnitude, is rlatively narrow. This applies above all at low rates of flow, e.g. low values of Reynolds Number, a situation that is typical in systems for the distribution of central-heating water. Another disadvantage is that the actuating forces which set the flap-like element of the known flowmeters in oscillatory motion are so small tht use must be made of means that are delicate, and therefore unsuitable in this connection, for converting the frequency of oscillation to a measure of the flow. As an example of such equipment, reference can be made to U.S. Pat. No. 2,453,376, in which an arm connected to the oscillation shaft passes between a source of light and a photoelectric cell. Thus, there exists need for a flowmeter in which the oscillating element is acted upon by such large actuating forces that the transmission of signals can take place in another way, for example by inductive means.